A metabolic model for the determination of shell composition in the bivalve mollusc, Mytilus edulis

Rosenberg. G. D. & Hughes, W. W. 1991 01 15: A metabolic model for the determination of shell composition in the bivalve mollusc, Mytilus edulis. Lethaia, Vol. 24. pp. 83–96. Oslo. ISSN 0024–1164. This research describes compositional variations within the shell of the extant mussel Mytilur edulis and proposes that they are produced by metabolic gradients within the shell-secreting mantle. Because we have previously proposed that the same metabolic gradients are responsible for variations in shell form (curvature), we establish here a model for molluscan shell growth integrating. for the first time. shell form and composition with mantle metabolism. The electron microprobe was used to measure the distribution of Mg. S, and Ca in the outer calcitic shell layer of sectioned. polished, and either A1- or C-coated shell. Mg/Ca and S/Ca ratios in the outer shell are respectively 1.25 and 1.40 times higher along slow-growing, commissure-umbo axes of high shell curvature and high metabolic activity than along rapidly growing axes of low curvature and low metabolic activity. The ratios within the inner surface of the calcitic shell layer decline most rapidly along commissure-umbo axes where mantle metabolic activity also declines rapidly. We reject the null hypothesis, generally at high levels of significance (1-tests. F-tests. regression analyses, and discriminant analysis. with p 4 0.01) that there is no difference in either Mg or S concentration in sections of the calcitic shell layer that differ in shell curvature and mantle metabolic activity. We conclude that calcium (mineral)-rich portions of shells are energctically less costly to produce than matrix or minor element-rich portions. in agreement with the proposal that natural selection favors mineral-rich shells because they are more efficient to produce than matrix-rich shells. Among-specimen differences are also highly significant (mixed model ANOVA). This confirms our assertion that paleontologists need to describe variations in skeletal composition among populations and throughout ontogeny as systematically as classical taxonomists describe morphology. if ever the environmental and the genetic influences on skeletal composition are to be distinguished. Bivalves. biomineralization, shell composition. magnesium, sulfur, calcium, metabolism, growth. Mytillus edulis     

The locomotion system of Mesozoic Coleoidea (Cephalopoda) and its phylogenetic significance

A morphological comparison of shell‐muscle contacts in coleoid cephalopods mainly from the Early Jurassic (Toarcian) Posidonia Shales of Holzmaden (Germany), the Middle Jurassic (Callovian) Oxford Clay of Christian Malford (UK), Late Jurassic (Kimmeridgian‐Tithonian) plattenkalks of Solnhofen (Germany), and the Late Cretaceous (Cenomanian) of Hâdjoula and Hâkel (Lebanon) provides new and meaningful insights into their locomotion systems. The study shows that both pro‐ostracum‐ and gladius‐bearing coleoids are typified by a marginal mantle attachment and by distinctly separated fins, which usually insert (indirectly via the shell sac and basal fin cartilages) to posterior shell parts. While absent in gladius‐bearing forms, mantle‐locking cartilages might have existed already in pro‐ostracum‐bearing belemnoids. Similar to ectocochleate ancestors, funnel‐ and cephalic retractors are generally attached to the internal (ventral) shell surface. A comparison of Mesozoic and Recent gladius‐bearing coleoids shows that the locomotion system (most significantly the dorsal mantle configuration, and the presence of nuchal‐ and funnel‐locking cartilages) is fundamentally different. This does not support the concept of ‘fossil teuthids’, but suggests, owing to similarities with Recent Vampyroteuthis, placement of Mesozoic gladius‐bearing coleoids within the Octobrachia (Octopoda + Vampyromorpha). Classification of Mesozoic gladius‐bearing coleoids as octobrachians implies that: (1) unambiguous teuthids are still unknown in the fossil record and (2) the similarity between Recent and some fossil gladiuses represents a matter of homoplasy.     

Development of the pedicle in the articulate brachiopod Terebratalia transversa (Brachiopoda,Terebratulida)

Summary The development of the pedicle in the articulate brachiopod Terebratalia transversa has been examined by electron microscopy. The posterior half of the free-swimming larva comprises a non-ciliated pedicle lobe that contains the primordium of the juvenile pedicle at its distal end. During settlement at five to six days post-fertilization, the pedicle lobe secretes a sticky sheet that attaches the larva to the substratum. As metamorphosis proceeds, the epithelium in the posterior half of the pedicle lobe produces a thin overlying cuticle, and the pedicle primordium develops into a stalk-like anchoring organ. The juvenile pedicle protrudes through the gape that occurs between the posterior margins of the shell valves. A cup-like canopy, called the pedicle capsule, lines the posterior end of the shell and surrounds the newly formed pedicle. The core of the juvenile pedicle is filled with a solid mass of connective tissue. Numerous tonofibrils occur in the pedicle epithelium, and the overlying cuticle consists of amorphous material covered by a thin granular fringe. By one year post-metamorphosis, a body cavity develops anterior to the pedicle. Two pairs of adjustor muscles extend from the posterior end of the shell and traverse the cavity to insert in the pedicle. The connective tissue core of the pedicle in sub-adult specimens lacks muscle cells but contains numerous fibroblasts and collagen fibers. Three regions are recognizable in the connective tissue compartment of the adult pedicle: a subepithelial layer of non-fibrous connective tissue, a central fibrous zone, and a proximal mass of tissue that resembles cartilage.List of abbreviations as adhesive sheet - bc body cavity - bv brachial valve of shell - cf collagen fibrils - ct connective tissue - cu cuticle - di diductor muscle - ec epithelial cell - f fibroblast - fz fibrous zone - g gut - gc granular cell - gd gastric diverticulum - ht hinge tooth - ia interarea of pedicle valve - icl inner cuticular layer - lo lophophore - lu lumen of gut - m mesenchyme - ma mantle - ml mantle lobe - ocl outer cuticular layer - p periostracum - pc pedicle capsule - pce pedicle capsule epithelium - pcl pedicle collar of shell - pcn pedicle connectives - pd pedicle - pe pedicle epithelium - pl pedicle lobe - pv pedicle valve of shell - pzc proximal zone of cartilage-like tissue - s substratum - sel subepithelial layer - t tendon - tf tonofibril - vam ventral adjustor muscle     

Tube construction in the watering pot shell Brechites vaginiferus (Bivalvia; Anomalodesmata; Clavagelloidea)

The bizarre watering pot shells of the clavagellid bivalve Brechites comprise a calcareous tube encrusted frequently with sand grains and other debris, the anterior end of which terminates in a convex perforated plate (the ‘watering pot’). It has not proved easy to understand how such extreme morphologies are produced. Previously published models have proposed that the tube and ‘watering pot’ are formed separately, outside the periostracum, and fuse later. Here we present the results of a detailed study of the structure and repair of the tubes of Brechites vaginiferus which suggest that these models are not correct. Critical observations include the fact that the external surface of the tube and ‘watering pot’ are covered by a thin organic film, on to the inner surface of which the highly organized aragonite crystals are secreted. There is no evidence of a suture between the tube and the ‘watering pot’ or that the periostracum of the juvenile shell passes through the wall of the tube. Live individuals of B. vaginiferus are able to repair substantial holes in the tube or ‘watering pot’ by laying down a new organic film followed by subsequent calcareous layers. Brechites vaginiferus displays Type C mantle fusion, with the result that the whole animal is encased by a continuous ring of mantle and periostracum, thereby making it possible to secrete a continuous ‘ring’ of shell material. On the basis of these observations we suggest that watering pot shells are not extra‐periostracal but are the product of simple modification of ‘normal’ shell‐secreting mechanisms.     

METABOLIC COMPARTMENTATION IN THE BRAIN: EFFECTS OF A CENTRAL NERVOUS SYSTEM DEPRESSANT, 1-HYDROXY-3-AMINO-PYRROLIDONE-2

—The effect of 1-hydroxy-3-aminopyrrolidone-2(HA-966), a CNS depressant, was studied on the metabolism of [¹⁴C]glucose and [³H]acetate in the brain in mice. HA-966 had a marked effect on glucose metabolism. The conversion of glucose carbon into amino acids associated with the tricarboxylic acid cycle (‘cycle’) was severely reduced, while the concentration of brain glucose was approximately doubled. Relative to the specific radioactivity of glucose in the brain, the specific radioactivity of alanine was 60–70 per cent of the control, indicating a reduction in the rate of glycolysis, and those of the‘cycle’amino acids were also lowered. A reduction in‘cycle’flux of 30–35 per cent was estimated. It was established that the depressed glucose utilization flux was not due to either impaired uptake of glucose from blood to brain or to hypothermia. In contrast to [¹⁴C]glucose, there was no change in the labelling of the amino acid fraction from [³H]acetate, which is preferentially metabolized in the 'small’compartment believed to be associated with glia. Thus it seems that CNS depression caused by HA-966 resulted in a selective decrease in energy production in the‘large’metabolic compartment where glucose is oxidized preferentially and which is believed to be associated with neuronal structures. The results also suggested that communication between the metabolic compartments mediated via glutamine and GABA was reduced, since the labelling from [³H]acetate of glutamine was increased and that of GABA decreased by HA-966.     

ONTOGENETIC NICHE SHIFT IN THE BRACHIOPOD TEREBRATALIA TRANSVERSA: RELATIONSHIP BETWEEN THE LOSS OF ROTATION ABILITY AND ALLOMETRIC GROWTH

Abstract: Many articulated brachiopods experience marked life habit variations during ontogeny because they experience their fluid environment at successively higher Reynolds numbers, and they can change the configuration of their inhalant and exhalant flows as body size increases. We show that the extant brachiopod Terebratalia transversa undergoes a substantial ontogenetic change in reorientation governed by rotation around the pedicle. T. transversa′s reorientation angle (maximum ability to rotate on the pedicle) decreases during ontogeny, from 180 degrees in juveniles to 10–20 degrees in individuals exceeding 5 mm, to complete cessation of rotation in individuals larger than 10 mm. Rotation ability is substantially reduced after T. transversa achieves the adult lophophore configuration and preferred orientation with respect to ambient water currents at a length of 2.5–5 mm. We hypothesize that the rotation angle of T. transversa is determined mainly by the position of ventral and dorsal points of attachment of dorsal pedicle muscles relative to the pedicle. T. transversa shows a close correlation between the ontogenetic change in reorientation angle and ontogeny of morphological traits that are related to points of attachment of dorsal pedicle muscles, although other morphological features can also limit rotation in the adult stage. The major morphological change in cardinalia shape and the observed reduction of rotation affect individuals 2.5–10 mm in length. The position of ventral insertions of dorsal pedicle muscles remains constant, but contraction of dorsal pedicle muscles is functionally handicapped because dorsal insertions shift away from the valve midline, rise above the dorsal valve floor, and become limited by a wide cardinal process early in ontogeny (<5 mm). The rate of increase of cardinal process width and of distance between dorsal pedicle muscle scars substantially decreases in the subadult stage (5–10 mm), and most of the cardinalia shell traits grow nearly isometrically in the adult stage (>10 mm). T. transversa attains smaller shell length in crevices than on exposed substrates. The proportion of small‐sized individuals and population density is lower on exposed substrates than in crevices, indicating higher juvenile mortality on substrates prone to grazing and physical disturbance. The loss of reorientation ability can be a consequence of morphological changes that strengthen substrate attachment and maximize protection against biotic or physical disturbance (1) by minimizing torques around the pedicle axis and/or (2) by shifting energy investments into attachment strength at the expense of the cost involved in reorientation.     

RABBIT SCIATIC NERVE FASCICLE AND''ENDONEURIAL''PREPARATIONS FOR IN VITRO STUDIES OF PERIPHERAL NERVE GLUCOSE METABOLISM

Abstract— Suitable preparations for in vitro studies of the composite glucose and energy metabolism of peripheral nerve axons and Schwann cells have not been available. Methods are described for the preparation and incubation of a defined segment of a rabbit sciatic nerve fascicle, free of epineurial contamination, but with an intact perineurial membrane; removing the perineurium provides in addition an‘endoneurial’preparation. Conditions were selected for incubating each preparation with glucose that maintained stable P-creatine and ATP concentrations and a stable rate of O₂ uptake; under these conditions the preparations retained an unaltered EM appearance during a 2-h incubation. Glucose diffusion into the endoneurial compartment of the fascicle is restricted, possibly by the perineurial membrane, and a higher medium glucose concentration (20 mM) was required to maintain a steady state of energy metabolism in this preparation than in the‘endoneurial’preparation, which was incubated with 5 mwglucose. The‘endoneurial’preparation required 0.50 mm -myoinositol in the medium to prevent a decrease in tissue free myoinositol and a slow decrease in O₂ uptake, which occurred when it was omitted. Under the incubation conditions selected the glucose concentrations in the‘endoneurial’preparation and in the endoneurial compartment of the fascicle were reasonably similar, and the preparations had similar rates of respiration, similar estimated rates of glucose utilization, and similar relative rates of respiration and lactate production. The preparations derive the major fraction of their energy requirements from respiration. Their rates of O₂ uptake are 60% higher than the previous indirect estimate of O₂ uptake in whole rabbit tibial nerve in situ. Constant rates of incorporation of ¹⁴C from [U-¹⁴C]glucose into CO₂ and total lipid were observed in the‘endoneurial’preparation after a 15-min equilibration period. The preparations reported provide suitable tools for in vitro studies of peripheral nerve metabolism not previously available.     

Sanitation with sponge and plunger: western Atlantic slit-wormsnails (Mollusca: Caenogastropoda: Siliquariidae)

Siliquariid Tenagodus (synonym: Siliquaria) snails are obligatory sponge commensals, with uncoiling and laterally slitted shells embedded inside Demospongiae hosts, and shell apertures facing the outside allowing for respiratory and gill‐filter‐feeding activities. Live‐collected animals observed in situ within hosts provide the first detailed functional morphological study of the group, and form the basis for systematic revision of the western Atlantic members of type genus Tenagodus (Siliquariidae, synonym: Tenagodidae). Three species are recognized. Overall anatomical features of wide‐ranging Atlantic T. modestus (Dall, 1881) and T. squamatus (de Blainville, 1827) [ = T. anguillae Mörch, 1861] are similar to those previously described for New Zealand Pyxipoma. A third species, Tenagodus barbadensis sp. nov. , is described from Barbados, based on shell characters. The three species live embedded in a few species of halichondriid and thrombid sponges at depths ranging from c. 20 to several hundred metres and show several characters not previously documented for the family. These include a short compressed‐S‐shaped osphradium, an anal opening positioned in the posterior mantle cavity, and cuspidate inner marginal radular teeth. Presence of shell septa sealing earlier parts of the shell, first described in the early 1800s but subsequently disputed, was verified. Observations on living T. squamatus demonstrated the use of the large tight‐fitting operculum in plunger‐like fashion, flushing the mantle cavity and discharging waste material (including faeces from the posteriorly located anus) through the shell slit into the host sponge's aquiferous canal system. Uncoiling shells, shell and mantle slits, and specialized opercular, gill and gut morphology are interpreted as adaptive traits of the sessile mode of life embedded in sponge tissue. Actively maintained linkage between snail and sponge water‐flow systems provides mutual benefits; these include the allowance for rapid defensive withdrawal and return‐to‐feeding position of the snail (by using the sponge canal system as a vent or reservoir for displaced water), sanitation of the mantle cavity (waste material can leave the snail through the shell slit at the posterior end of the mantle cavity, avoiding fouling of the gill‐feeding system), and by providing increased water flow and, potentially, extra nutritional particles for the sponge (food and waste particles stemming from the snail's activity). The lectotypes selected herein are Serpula anguina Linnaeus, 1758, Tenagodus anguillae Mörch, 1861, and Siliquaria modesta Dall, 1881. © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society, 2004, 140 , 307–333.     

Homeobox gene expression in Brachiopoda: the role of Not and Cdx in bodyplan patterning, neurogenesis, and germ layer specification

The molecular control that underlies brachiopod ontogeny is largely unknown. In order to contribute to this issue we analyzed the expression pattern of two homeobox containing genes, Not and Cdx, during development of the rhynchonelliform (i.e., articulate) brachiopod Terebratalia transversa. Not is a homeobox containing gene that regulates the formation of the notochord in chordates, while Cdx (caudal) is a ParaHox gene involved in the formation of posterior tissues of various animal phyla. The T. transversa homolog, TtrNot, is expressed in the ectoderm from the beginning of gastrulation until completion of larval development, which is marked by a three-lobed body with larval setae. Expression starts at gastrulation in two areas lateral to the blastopore and subsequently extends over the animal pole of the gastrula. With elongation of the gastrula, expression at the animal pole narrows to a small band, whereas the areas lateral to the blastopore shift slightly towards the future anterior region of the larva. Upon formation of the three larval body lobes, TtrNot expressing cells are present only in the posterior part of the apical lobe. Expression ceases entirely at the onset of larval setae formation. TtrNot expression is absent in unfertilized eggs, in embryos prior to gastrulation, and in settled individuals during and after metamorphosis. Comparison with the expression patterns of Not genes in other metazoan phyla suggests an ancestral role for this gene in gastrulation and germ layer (ectoderm) specification with co-opted functions in notochord formation in chordates and left/right determination in ambulacrarians and vertebrates. The caudal ortholog, TtrCdx, is first expressed in the ectoderm of the gastrulating embryo in the posterior region of the blastopore. Its expression stays stable in that domain until the blastopore is closed. Thereafter, the expression is confined to the ventral portion of the mantle lobe in the fully developed larva. No TtrCdx expression is detectable in the juvenile after metamorphosis. This expression of TtrCdx is congruent with findings in other metazoans, where genes belonging to the Cdx/caudal family are predominantly localized in posterior domains during gastrulation. Later in development this gene will play a fundamental role in the formation of posterior tissues.     

Mechanical strength of shells of selected extant articulate brachiopods: Implications for paleozoic morphologic trends

Dried shells of Terebratalia transversa, Laqueus californianus, Hemithyris psittacea, and T. unguicula and alcohol‐soaked, tissue‐lined shells of Terebratulina retusa, Dallina septigera, Cryphus vitreus, and Liothyrella uva were crushed in an apparatus that facilitated measurement of the force (newtons) against the valves at the instant of fracture. The results revealed that the costate shells of T. transversa and T. retusa were the strongest. Force is correlated with valve thickness, but not with size (length). When normalized for valve thickness, the force required to fracture shells is correlated with shell biconvexity (height/length) among pooled species of dried specimens. Geniculate specimens of T. retusa were not stronger than the intraspecific variants with a constant radius of curvature to their valves.

The percent‐frequency of plicate, spinose, lamellose and rugate genera increase significantly in the successive stages, Caradocian (Late Ordovician) through Famennian (Late Devonian) at the expense of smooth to costellate genera. The percent‐frequency of rectimarginate (central fold lacking) genera also decreases appreciably in this time frame. These morphologic trends, in combination with the experimental crushing data, support the hypothesis that selection favored species with such anti‐predatory adaptations during a time of escalation of shell‐crushing predators.     

Description of two new miniature species of Hylopanchax Poll & Lambert, 1965 (Cyprinodontiformes: Procatopodidae), from northeastern Gabon,with an updated diagnosis of the genus based on morphology,colouration and osteology

Two new species of the lampeye genus Hylopanchax are described from the Ivindo River basin in the Ogowe River drainage. Hylopanchax multisquamatus, new species, and Hylopanchax thysi, new species, differ from congeners by the presence of a hyaline urogenital male papilla with small black spots and a dark-brown reticulate pattern on the flanks of both males and females in preserved specimens. Hylopanchax multisquamatus is distinguished from congeners by the number of scales on the mid-longitudinal series (27–30 vs. 19–26, respectively) and by the relative anterior/posterior flank scale depth ratio (140%–150% vs. 170%–220%). Hylopanchax thysi is distinguished from all other congeners, except Hylopanchax paucisquamatus, by the presence of vertebrae (30 vs. 31–33) and is further distinguished from H. multisquamatus by the presence of a deeper caudal peduncle and much larger anterior flank scales. It is distinguished from H. paucisquamatus by the presence of a hyaline urogenital male papilla with small black spots and a dark-brown reticulate pattern on the flanks of both males and females in preserved specimens. Osteological data of Hylopanchax are presented for the first time, and an updated diagnosis based on external morphology, colouration pattern and osteology is provided. An osteological comparison with closely related species belonging to the genera Procatopus, Hypsopanchax and “Hypsopanchax” is presented. (a) A truncate and slightly downward-directed anterior process of the angulo-articular and (b) a guitar-shaped lachrymal with both its anterior and posterior margins sharply curved are here considered as diagnostic features of Hylopanchax.     

乳酸脱氢酶基因调控对HEK-293细胞代谢和腺病毒生产的影响

减少乳酸积累一直是哺乳动物细胞生物技术产业的一个目标。体外培养动物细胞时,乳酸积累主要是2种代谢途径作用的综合结果:一方面,葡萄糖在乳酸脱氢酶A(lactate dehydrogenase A,LDHA)的作用下生成乳酸;另一方面,乳酸可通过乳酸脱氢酶B(LDHB)或乳酸脱氢酶C(LDHC)氧化为丙酮酸重新进入三羧酸循环。本研究综合评估了乳酸代谢关键基因调控对人胚胎肾细胞(human embryonic kidney 293 cells,HEK-293)细胞生长、代谢和人腺病毒(human adenovirus,HAdV)生产的影响,有效提高了HEK-293细胞的HAdV生产能力,并为哺乳动物细胞的乳酸代谢工程调控提供了理论基础。通过改造乳酸代谢关键调控基因(敲除ldha基因以及过表达ldhb和ldhc基因),有效改善了HEK-293细胞的物质和能量代谢效率,显著提高了HAdV的生产。与对照细胞相比,3个基因改造均能促进细胞生长,降低乳酸和氨的积累,明显增强细胞的物质和能量代谢效率,显著提高了HEK-293细胞的HAdV生产能力。ldhc基因过表达对HEK-293细胞的生长、代谢和HAdV生产调控最显著,最大细胞密度提高了约38.7%,乳酸对葡萄糖得率和氨对谷氨酰胺得率分别下降了33.8%和63.3%,HAdV滴度提高了至少16倍。此外,相比于对照细胞株,改造细胞株的腺苷三磷酸(adenosine triphosphate,ATP)生成速率、ATP/O_(2)比率、ATP与腺苷二磷酸(adenosine diphosphate,ADP)的比值以及还原型辅酶Ⅰ(nicotinamide adenine dinucleotide,NADH)含量均有不同程度的提高,能量代谢效率明显改善。     

BRACHIOPOD PALAEOECOLOGY IN MIDDLE DANIAN LIMESTONES AT FAKSE, DENMARK

The Danian limestone in the Fakse quarry displays banks of coral limestone interfingering with banks of bryozoan limestone. (1) Previous and present studies on the brachiopods show that ‘Rhynchonella’ flustracea Buch, ‘R.’ faxensis Posselt, ‘Terebratula’ mobergi Lundgren, and Argyrotheca pindborgi (Nielsen) are restricted to the coral limestone of Fakse. (2) Crania (Danocrania) transversa (Lundgren), C. (D.) tuberculata (Nilsson), Isocrania aff. egnabergensis (Retzius), ‘Terebratula’ fallax Lundgren, and Carneithyris incisa (Buch) are known from bryozoan limestone at Fakse and other Middle Danian localities. (3) Common to both kinds of sediments in Fakse quarry and found at other Middle Danian bryozoan limestone localities as well are Terebratulina aff. chrysalis (Schlotheim), Argyrotheca scabricula (Koenen), Megathiris bruennichi (Rosenkrantz), Platidia sp., and Thecidellina? groenwalli (Nielsen). (4) ‘Terebratula cincta’ Nielsen is restricted to Fakse quarry and occurs in both kinds of sediments. (5) Some of the species restricted to the coral limestone appear to be morphologically adapted to fit in between the branches of the dominant coral in Fakse quarry, Dendrophyllia candelabrum Hennig.     

SHAPE AND FUNCTION OF THE SHELL: A COMPARISON OF SOME LIVING AND FOSSIL BIVALVE MOLLUSCS

• 1 The review is mainly concerned with Carboniferous non-marine Anthracosiidae and Myalinidae, of which only the shells are known, and with certain unspecialized non-byssate suspension-feeding bivalves which had smooth shells and burrowed shallowly.
• 2 Limited experimental evidence and observation of living bivalves suggest that in certain Recent siphonate species and in some members of the non-siphonate Anthracosiidae the shape of the shell was functionally related to movement through the sediment in the same way. Predicted optimum shapes of shells for downward burrowing and for upward near-vertical movement in sands and silts were apparently realized in the Anthracosiidae, which constituted a series of highly variable opportunistic assemblages. It is stressed, however, that the shape of the shell always appears to be a compromise between several functional requirements.
• 3 In both the early Anthracosiidae and in several analogous Recent marine genera, orientation of the long axis of the shell was the same for downward burrowing and for upward pushing, that is near the vertical, with posterior end upward.
• 4 Invasion of the Pennine late-Namurian delta took place when marine bivalves pushed upward, thereby avoiding sedimentation from delta lobes moving seaward relatively swiftly. The evolution of Carbonicola occurred at about this time (the Marsdenian Age) when the bivalves acquired a smooth elongate shell of ‘streamlined’ form, having a hinge plate with swellings and depressions on it (later to evolve into teeth). All these features tend to characterize the active shallow burrowers of today.
• 5 Entry into soft-bottom eutrophic conditions of fresh water is characterized in several unionids by increase in height/length (H/L or w/m) ratio of shell, in anterior end/length (A/L) and in obesity (T/L) (see Fig. 2, centre). These changes also took place in established faunas of Carbonicola characteristic of richly carbonaceous shales, in faunas of supposed Anthraconaia in more carbonaceous sediments of mid-and late-Carboniferous times in the U.S.A. and in Anthraconauta of the British late Carboniferous (Westphalian C and D). The genus Anthracosphaerium epitomizes the culmination of these trends in the Anthracosiidae, and species of the genus were probably epifaunal or shallowly infaunal active burrowers on soft bottoms in Westphalian upper A and B time.
• 6 Two contrasting patterns of growth characterize the shells of the widely variable unionid Margaritifera margaritifera. In the first, dorsal arching of the shell, with straightening and reflexion of the ventral margin, provides increased weight but decreased ligamental strength. In the second, in which the ‘hinge line’ tends to remain straight while the dorsal margin becomes more rounded and obesity increases, there is increased metabolic efficiency for active surface movement. The maintenance of these trends within the species, which may be regarded as secondarily opportunistic, affords a means of insurance for survival within the highly variable environments of fresh water. The same trends are recognizable in established faunas of Carbonicola, where it is likely that they performed the same function, as well as in Mesozoic and Cenozoic Unionidae.
• 7 The functional explanation outlined in paragraph (6) may be extended to provide an ecological meaning for Ortmann's ‘Law of Stream Distribution’, which states that obesity of unionid shells increases downstream. This applies broadly, within a fairly wide range of variation, a fact which again suggests ‘insurance’ of faunas against the variable hazards of fresh-water habitats.
• 8 In bivalves having considerable thickness of shell in relation to their size, and having strong umbonal development, specific gravity of the living bivalve is correlated with H/L and T/L ratios of the shell, as in the venerid Venerupis rhomboides. In this species, differences in the specific gravities of the bivalves, as well as their shape, appear to be functionally related to shallowly infaunal burrowing in different substrates.
• 9 The conclusions of paragraphs 6 and 8 provide a functional explanation, in terms of selection, for the palaeoecological ‘law’ of Eagar (1973), which is applicable to established faunas of Carbonicola in mid-Carboniferous time, and relates variational trends in two main groups of shells primarily to increases in the relative water velocities of the palaeoenvironments.
• 10 Where the growth of relatively unspecialized bivalve shells has been measured, allometric relationships have usually been found in H-L and T-L scatters. Logarithmic lines have two inflexions and linear scatters a sigmoidal form. A similar pattern of allometric growth has been found in both Carbonicola (H-L) and Anthraconauta (m-w). These patterns appear to be related to the optimum requirements of water-borne larvae, the initial byssal phase of settlement, when ability to burrow quickly is essential, and the main period of growth and activity. It is herein suggested that the final second inflexion, which indicates a falling off of gain in H/L and T/L ratios, may be a genetically controlled modification of the growth pattern which counteracts the operation of the ‘cube-square rule’ (of Thompson, 1942) and prolongs productive life.
• 11 Patterns of relative growth of the shell may be significantly modified by conditions of the habitat; both T/L and H/L ratios may be increased, with general reduction in size, in the less ‘favourable’ habitats. Both these ratios have been similarly modified, the one in the ‘natural laboratory’ of a lake formed by the damming up of streams, and the other in transplant experiments with living Venerupis. In both these latter cases, phenotypic changes took place in the same direction as those expected on the basis of natural selection. Direct response to environmental factors cannot therefore be ruled out as an agent in similar changes noted in Carbonicola and supposed Anthraconaia in paragraphs (5) and (9) and may have been operative in those of paragraphs (7) and (8).

     

The biology and functional morphology of Arca noae (Bivalvia: Arcidae) from the Adriatic Sea, Croatia, with a discussion on the evolution of the bivalve mantle margin

In the Croatian Adriatic, Arca noae occurs from the low intertidal to a depth of 60 m; it can live for > 15 years and is either solitary or forms byssally attached clumps with Modiolus barbatus. The shell is anteriorly foreshortened and posteriorly elongate. The major inhalant flow is from the posterior although a remnant anterior stream is retained. There are no anterior but huge posterior byssal retractor muscles and both anterior and posterior pedal retractors. The ctenidia are of Type B(1a) and the ctenidial–labial palp junction is Category 3. The ctenidia collect, filter and undertake the primary sorting of potential food in the inhalant water. The labial palps are small with simple re‐sorting tracks on the ridges of their inner surfaces. The ciliary currents of the mantle cavity appear largely concerned with the rejection of particulate material. The mantle margin comprises an outer and an (either) inner or middle fold. The outer fold is divided into outer and inner components that secrete the shell and are photo‐sensory, respectively. The latter bears a large number of pallial eyes, especially posteriorly. The inner/middle mantle fold of A. noae, possibly representative of simpler, more primitive conditions, may have differentiated into distinct folds in other recent representatives of the Bivalvia.     

Metabolic depression in animals: physiological perspectives and biochemical generalizations

Depression of metabolic rate has been recorded for virtually all major animal phyla in response to environmental stress. The extent of depression is usually measured as the ratio of the depressed metabolic rate to the normal resting metabolic rate. Metabolic rate is sometimes only depressed to approx. 80% of the resting value (i.e. a depression of approx. 20% of resting); it is more commonly 5-40 % of resting (i.e. a depression of approx. 60-95% of resting); extreme depression is to 1% or less of resting, or even to an unmeasurably low metabolic rate (i.e. a depression of approx. 99-100% of resting). We have examined the resting and depressed metabolic rate of animals as a function of their body mass, corrected to a common temperature. This allometric approach allows ready comparison of the absolute level of both resting and depressed metabolic rate for various animals, and suggests three general patterns of metabolic depression. Firstly, metabolic depression to approx. 0.05-0.4 of rest is a common and remarkably consistent pattern for various non-cryptobiotic animals (e.g. molluscs, earthworms, crustaceans, fishes, amphibians, reptiles). This extent of metabolic depression is typical for dormant animals with ‘intrinsic’ depression, i.e. reduction of metabolic rate in anticipation of adverse environmental conditions but without substantial changes to their ionic or osmotic status, or state of body water. Some of these types of animal are able to survive anoxia for limited periods, and their anaerobic metabolic depression is also to approx. 0.05-0.4 of resting. Metabolic depression to much less than 0.2 of resting is apparent for some ‘resting’, ‘over-wintering’ or diapaused eggs of these animals, but this can be due to early developmental arrest so that the egg has a low ‘metabolic mass’ of developed tissue (compared to the overall mass of the egg) with no metabolic depression, rather than having metabolic depression of the entire cell mass. A profound decrease in metabolic rate occurs in hibernating (or aestivating) mammals and birds during torpor, e.g. to less than 0.01 of pre-torpor metabolic rate, but there is often no intrinsic metabolic depression in addition to that reduction in metabolic rate due to readjustment of thermoregulatory control and a decrease in body temperature with a concommitant Q₁₀ effect. There may be a modest intrinsic metabolic depression for some species in shallow torpor (to approx. 0.86) and a more substantial metabolic depression for deep torpor (approx. 0.6), but any energy saving accruing from this intrinsic depression is small compared to the substantial savings accrued from the readjustment of thermoregulation and the Q₁₀ effect. Secondly, a more extreme pattern of metabolic depression (to < 0.05 of rest) is evident for cryptobiotic animals. For these animals there is a profound change in their internal environment-for anoxybiotic animals there is an absence of oxygen and for osmobiotic, anhydrobiotic or cryobiotic animals there is an alteration of the ionic/osmotic balance or state of body water. Some normally aerobic animals can tolerate anoxia for considerable periods, and their duration of tolerance is inversely related to their magnitude of metabolic depression; anaerobic metabolic rate can be less than 0.005 of resting. The metabolic rate of anhydrobiotic animals is often so low as to be unmeasurable, if not zero. Thus, anhydrobiosis is the ultimate strategy for eggs or other stages of the life cycle to survive extended periods of environmental stress. Thirdly, a pattern of absence of metabolism when normally hydrated (as opposed to anhydrobiotic or cryobiotic) is apparently unique to diapaused eggs of the brine-shrimp (Artemia spp., an anostracan crustacean) during anoxia. The apparent complete metabolic depression of anoxic yet hydrated cysts (and extreme metabolic depression of normoxic, hypoxic, or osmobiotic, yet hydrated cysts), is an obvious exception to the above patterns. In searching for biochemical mechanisms for metabolic depression, it is clear that there are five general characteristics at the molecular level of cells which have a depressed metabolism; a decrease in pH, the presence of latent mRNA, a change in protein phosphorylation state, the maintenance of one particular energy-utilizing process (ion pumping), and the down-regulation of another (protein synthesis). Oxygen sensing is now the focus of intense investigation and obviously plays an important role in many aspects of cell biology. Recent studies show that oxygen sensing is involved in metabolic depression and research is now being directed towards characterising the proteins and mechanisms that comprise this response. As more data accumulate, oxygen sensing as a mechanism will probably become the sixth general characteristic of depressed cells. The majority of studies on these general characteristics of metabolically depressed cells come from members of the most common group of animals that depress metabolism, those non-cryptobiotic animals that remain hydrated and depress to 0.05-0.4 of rest. These biochemical investigations are becoming more molecular and sophisticated, and directed towards defined processes, but as yet no complete mechanism has been delineated. The consistency of the molecular data within this group of animals suggests similar metabolic strategies and mechanisms associated with metabolic depression. The biochemical ‘adaptations’ of anhydrobiotic organisms would seem to be related more to surviving the dramatic reduction in cell water content and its physico-chemical state, than to molecular mechanisms for lowering metabolic rate. Metabolic depression would seem to be an almost inevitable consequence of their altered hydration state. The unique case of profound metabolic depression of hydrated Artemia spp. cysts under a variety of conditions could reflect unique mechanisms at the molecular level. However, the available data are not consistent with this possibility (with the exception of a uniquely large decrease in ATP concentration of depressed, hydrated Artemia spp. cysts) and the question remains: how do cells of anoxic and hydrated Artemia spp. differ from anoxic goldfish or turtle cells, enabling them so much more completely to depress their metabolism?     

A new method to determine the energy saving night temperature for vegetative growth of Phalaenopsis

Knowledge of the energy saving night temperature (i.e. a relatively cool night temperature without affecting photosynthetic activity and physiology) and a better understanding of low night temperature effects on the photosynthetic physiology of Phalaenopsis would improve their production in terms of greenhouse temperature control and energy use. Therefore, Phalaenopsis‘Hercules’ was subjected to day temperatures of 27.5°C and night temperatures of 27.0°C, 24.2°C, 21.2°C, 18.3°C, 15.3°C or 12.3°C in a growth chamber. A new tool for the determination of the energy saving night temperature range was developed based on temperature response curves of leaf net CO₂ exchange, chlorophyll fluorescence, organic acid content and carbohydrate concentrations. The newly developed method was validated during a complete vegetative cultivation in a greenhouse environment with eight Phalaenopsis hybrids (i.e. ‘Boston’, ‘Bristol’, ‘Chalk Dust', ‘Fire Fly’, ‘Lennestadt’, ‘Liverpool’, ‘Precious’, ‘Vivaldi’) and day/night temperature set points of 28/28°C, 29/23°C and 29/17°C. Temperature response curves revealed an overall energy saving night temperature range for nocturnal CO₂ uptake, carbohydrate metabolism, organic acid accumulation and photosystem II (PSII) photochemistry of 17.1°C to 19.9°C for Phalaenopsis‘Hercules’. At the lower end of this energy saving night temperature range, a high malate‐to‐citrate ratio switched towards a low ratio and this transition seemed to alleviate effects of night chilling induced photoinhibition. At night temperatures of 24°C or higher, the degradation of starch, glucose and fructose indicated an increased respiratory CO₂ production. During the greenhouse validation experiment, the differences between the eight Phalaenopsis hybrids with regard to their response to the warm day/cool night temperature regimes were remarkably large. In general, the day/night temperature of 29/17°C led to a significantly lower biomass accumulation and less leaves which were in addition shorter, narrower and smaller in size as compared to the day/night temperature regimes of 28/28°C and 29/23°C. During week 25 of the cultivation period, plants matured and flower initiation steeply increased for all hybrids and in each day/night temperature regime. Before week 25, early spiking was only sufficiently suppressed in the 29/23°C and 29/17°C temperature regimes for three hybrids (‘Boston’, ‘Bristol’ and ‘Lennestadt’) but not in the other five hybrids. Although a considerable biochemical flexibility was demonstrated for Phalaenopsis‘Hercules’, inhibition of flowering after exposure to a combination of warm days and cool nights appeared to be largely hybrid dependent.